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NOTE: THE UNIVERSITY PCs HAVE VERSION 11.0 – YOU MAY NEED TO DOWNLOAD THIS VERSION AND NOT THE LATEST VERSION TO ALLOW COMPATIBILITY BETWEEN SOFTWARE DEVELOPED IN THE LAB AND AT HOME. Ladder Logic (Digital) Ladder logic programs were designed to mimic the electrical circuit diagrams used for wiring control systems in the electrical industry when relay control was primarily used. The basic purpose of an electrical control system is to determine whether a load should be turned ON or turned OFF, under what circumstances and when it should happen. To understand a ladder program we need to remember the concept of current flow - a load is turned ON when the current can flow to it and is turned OFF when the current cannot flow to it. Below is an example of a relay logic diagram: The physical appearance of the logic resembles a ladder with each line of logic forming a “rung”. The digital input element of a ladder diagram is a "Contact". A contact has only two states: open or closed. An open contact breaks the current flow whereas a closed contact allows current to flow through it to the next element. The simplest example of a contact is an ON/OFF switch, which requires external force to activate it (either human or mechanical). Limit switches are those small switches that are placed at certain location so that when a mechanical device moves towards it, the contact will be closed and when the device moves away from it, the contact will be open. Symbol for a Normally Open Contact: The digital output elements are referred to as coils. The coils of a relay are energised then the output is said to be ON. 5 | P a g e
Symbol for a Coil: If a contact is connected to a coil and the contact is closed, the coil will be turned ON. This simple concept can be illustrated by the most basic ladder diagram as follow: There are various versions of coils and contacts available, which perform in different ways. We will look at some of them in this series of lab sessions however, the full programming manual is available at - e.pdf This document is over 700 pages long so think twice about printing! 6 | P a g e
Lab 1 - Connected Components Workbench (CCW) Introduction In this first lab session we will explore the basics of the programming software CCW and produce a simple ladder logic program. We can then test the program by connecting a Micro820 PLC, downloading the program and connecting input and output devices Instructions Start by opening the CCW software. If programming on the terraces you will find it in FAS software. Begin a new project by clicking on Catalog and expanding the Controllers folder in the Device Toolbox , which is located on the right-hand side of the Workbench screen. Double click on a Controller. For these labs we will be using the 2080-LC20-20QWB or the 2080-LC20-20QBB : You will be asked to verify the version of the controller which is currently version 10. Click OK A new Micro820 project based on this controller has now been created. The Micro820 should be shown in the Project Organiser on the left-hand side of the Workbench screen.
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- Summer '18
- Brett Gordon
- ladder logic